JPH06331498A - Abnormality detector in load control device - Google Patents

Abstract

PURPOSE:To judge the abnormality due to the deterioration of load and at the same time improve the judgment accuracy of abnormality. CONSTITUTION:An ECU 24 is provided with a microcomputer 28, a buffer 29. and a heater conduction circuit 30 and a heater 16 of an oxygen sensor is connected to the heater conduction circuit 30. In the heater conduction circuit 30, a battery 25, the heater 16, a protective resistance RP, and a transistor Tr1 are connected in series and at the same time a shunt resistor RT is connected in series with the heater 16 and in parallel with the protective resistor RP and the transistor Tr1. The heater 16 is subjected to conduction control according to the ON/OFF operation of the transistor Tr1. The shunt resistor RT detects the current value of the heater 16 as a voltage value. Also, comparators 33 and 34 compare a detection voltage VHD at a connection point P with threshold values VTH1 and VTH2 and then outputs the judgment result. The microcomputer 28 judges the abnormality due to the deterioration of the heater 16 and the abnormality in the heater control system according to output signals C1 and C2 of the comparators 33 and 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load control apparatus for controlling a load such as a resistance load such as a heater used in an oxygen sensor or a coil load such as a solenoid valve used in a fuel injection valve. The present invention relates to an abnormality detection device in a load control device for detecting the deterioration of the load and an abnormality that occurs in the load control system.

[0002]

2. Description of the Related Art Conventionally, as an abnormality detecting device for detecting an abnormality of a load control system, for example, Japanese Patent Application Laid-Open No. 3-1652.
No. 45 and Japanese Utility Model Laid-Open No. 62-153566 are disclosed.

In the abnormality detecting device disclosed in Japanese Patent Laid-Open No. 3-165245, the heater (load) for heating the oxygen sensor is energized and controlled in accordance with the on / off operation of the transistor (switching element). The current value when the heater is turned on is detected, and the heater control system abnormality is determined based on the current value of the heater.

On the other hand, in the abnormality detecting device disclosed in Japanese Utility Model Laid-Open No. 62-153566, the heater (load) of the oxygen sensor is duty-controlled by the controller and the ground side voltage of the heater is smoothed by using a smoothing circuit. It was smoothing. Then, the controller detects the abnormality of the heater control system based on the comparison between the heater voltage assumed by the control duty and the actual average heater voltage output from the smoothing circuit.

[0005]

However, the above-mentioned conventional abnormality detecting device has the following problems. That is, in Japanese Patent Laid-Open No. 3-165245, since the heater abnormality is detected when the heater is turned on,
The current flowing through the heater changes greatly under the influence of the switching element loss (ON resistance, saturation voltage). In particular, when the deterioration level of the heater is small, the current of the heater is greatly affected by the loss of the switching element described above, so that the detection accuracy of the current value is reduced, and accordingly, the accuracy of the abnormality determination may be reduced.

Further, in Japanese Utility Model Laid-Open No. 62-153566, there is a problem that the heater abnormality cannot be detected when the condition of 100% driving duty to the heater continues for a long time, and the smoothing circuit is sufficiently smooth. In order to have a function, it was necessary to set a large time constant, and there was a problem in terms of responsiveness.

In addition, in the above-mentioned conventional abnormality detecting apparatus, it is impossible to detect abnormality due to load deterioration by simply detecting normality / abnormality of load, and there is a demand for an apparatus capable of detecting deterioration abnormality. It was rare.

The present invention has been made in view of the above problems, and an object thereof is to make it possible to determine an abnormality due to deterioration of a load and to improve the accuracy of the abnormality determination. An object is to provide an abnormality detection device in a load control device.

[0009]

In order to achieve the above object, a first invention is to connect a power source, a load and a switching element in series, and to connect the load according to ON / OFF operation of the switching element. Used in a load control device for energizing or interrupting, in series with the load,
And, when the current detection resistor connected in parallel to the switching element and the energization of the load are interrupted, if the current value of the load detected by the current detection resistor is equal to or less than a predetermined threshold value. The gist of the present invention is to provide an abnormality determining means for determining that an abnormality has occurred in the load.

A second aspect of the present invention is used in a load control device in which a power source, a load and a switching element are connected in series, and the load is energized or cut off according to the on / off operation of the switching element. Which is in series with the load, and a resistance for current detection connected in parallel to the switching element, and when the energization of the load is cut off, of the load detected by the resistance for current detection If the current value is equal to or lower than a predetermined threshold value, it is determined that an abnormality has occurred in the load, and when the load is energized, if the current value of the load is equal to or higher than a predetermined threshold value, the load The gist of the present invention is to include an abnormality determining means for determining that an abnormality has occurred in the control system.

Further, in the first or second invention, the threshold value for determining the current value of the load may be provided in a plurality of stages. Further, the abnormality detection may be prohibited when the voltage value of the power source is a predetermined value or less.

[0012]

According to the first aspect of the present invention, the load is energized when the switching element is turned on, and the load is deenergized when the switching element is turned off. Further, the current value of the load when the energization of the load is cut off is detected by the current detection resistor connected in series with the load and in parallel with the switching element. Then, the abnormality determining means determines that an abnormality has occurred in the load when the current value of the load is equal to or less than a predetermined threshold value when the energization of the load is cut off.

That is, for example, when the deterioration of the load progresses with the lapse of time, the internal resistance of the load increases and the current value decreases. Therefore, the abnormality determination unit detects the decrease in the current value of the load to determine the abnormality associated with the deterioration. Further, since this abnormality determination is performed when the energization of the load is cut off (when the switching element is off), the current value of the load is detected without being affected by the loss such as the on resistance of the switching element, and the current value The detection accuracy is improved and the accuracy of abnormality determination is improved.

Further, according to the second aspect of the invention, the abnormality determining means is configured to detect the load if the current value of the load detected by the current detecting resistor is equal to or less than a predetermined threshold value when the load is de-energized. It is determined that an abnormality has occurred in the load control system if the current value of the load is equal to or greater than a predetermined threshold value when the load is energized.

That is, according to the second aspect of the invention, similarly to the first aspect of the invention, when the energization of the load is cut off, it is possible to determine the abnormality due to the deterioration of the load, and at the time of energizing the load, the load control is performed. It is possible to judge the abnormality that occurs in the system.

Further, by providing thresholds for determining the current value of the load in a plurality of stages, it is possible to determine the degree of load deterioration and control system abnormality. Further, by prohibiting the abnormality detection when the voltage value of the power supply is equal to or lower than the predetermined value, erroneous detection can be prevented.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying an abnormality detecting device in a load control device according to the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing a schematic structure of a multi-cylinder spark ignition type gasoline engine mounted on a vehicle. In FIG. 2, a cylinder 4 is provided in an engine body 1 composed of a cylinder head 2 and a cylinder block 3, and a piston 5 is fitted in the cylinder 4. An intake passage 8 and an exhaust passage 9 are connected to the engine body 1 via an intake valve 6 and an exhaust valve 7. In the cylinder 4, a cylinder head 2, a cylinder block 3, a piston 5, an intake valve 6
A combustion chamber 10 is formed by being surrounded by the exhaust valve 7 and the like, and the combustion chamber 10 is provided with a spark plug 11. Water jacket 27 provided on the cylinder block 3
A water temperature sensor 26 is provided in the
Outputs a water temperature signal TW corresponding to the temperature of the cooling water in the water jacket 27.

In the intake passage 8, from the upstream side thereof,
An air filter 12 that purifies intake air, an air flow meter 13 that detects the amount of intake air, a throttle valve 14 that opens and closes the intake passage 8 in conjunction with an accelerator pedal, and fuel that is pressure-fed from a fuel supply unit to the intake passage 8. Fuel injection valves 15 for injecting toward the intake port portion forming the downstream portion are provided respectively.

In the exhaust passage 9, from the upstream side thereof,
Oxygen sensor 17, three-way catalytic converter 18 for purifying exhaust gas, and silencer 19 for silencing exhaust noise
Is provided. The oxygen sensor 17 is provided with a heater 16 as a load in this embodiment. The oxygen sensor 17 becomes active when the temperature of the sensor 17 exceeds approximately 650 ° C. Then, when the air-fuel ratio of the air-fuel mixture that normally operates in this active state and is used for combustion in the combustion chamber 10 is close to the stoichiometric air-fuel ratio, the rich side and the lean side are used as a boundary. Outputs a binary oxygen concentration signal V02 having different levels.

Further, the engine body 1 is provided with a distributor 20 whose rotary shaft is rotationally driven by a crankshaft. The distributor 20 is provided with a crank angle sensor 21, and the crank angle sensor 21 outputs a crank angle signal SC according to the rotation speed of the engine. Further, the distributor 20 is connected to an ignition coil unit 23 integrated with the ignition timing control unit 22.

Electronic control unit (hereinafter referred to as ECU) 24
Is the fuel injection by the fuel injection valve 15 and the spark plug 1.
1 for controlling each ignition, and the battery voltage VB from the battery 25 which is a power source.
Drive at (12V). The intake air amount signal SM from the air flow meter 13, the crank angle signal SC from the crank angle sensor 21, the oxygen concentration signal VO2 from the oxygen sensor 17, the water temperature signal TW from the water temperature sensor 26, etc. are input to the ECU 24. It Then, the ECU 24 executes fuel injection control and ignition timing control based on the output signals (SM, SC, VO2, TW) from various sensors. Further, in the present embodiment, the ECU 24 is configured to carry out energization control and abnormality determination of the heater 16 attached to the oxygen sensor 17 (details will be described later).

Here, the fuel injection control by the ECU 24 will be described. When the operating condition of the engine satisfies a predetermined condition, for example, when the operating condition is neither the acceleration condition nor the deceleration condition, the high load / high rotation condition, and the starting condition, the ECU 24 receives the intake air amount signal. The basic fuel injection amount is calculated according to SM and the crank angle signal SC. Further, the ECU 24 corrects the basic fuel injection amount based on the oxygen concentration signal VO2 from the oxygen sensor 17, and generates an injection pulse signal CP having a pulse width corresponding to the fuel injection amount. In making this correction, the ECU 24
When the oxygen concentration signal VO2 detects that the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio, the basic fuel injection amount is increased by a predetermined amount, and it is detected that it is on the rich side. If so, the basic fuel injection amount is reduced by a predetermined amount. As a result, feedback control of the air-fuel ratio is performed so that the actual air-fuel ratio converges to the theoretical air-fuel ratio which is the target air-fuel ratio. Then, the fuel injection valve 15 is opened only during the period corresponding to the pulse width of the injection pulse signal CP, and the amount of fuel corresponding to the operating state of the engine is injected into the intake port portion.

Explaining the ignition timing control by the ECU 24, the ECU 24 sets the ignition timing (normal ignition timing) according to the operating condition of the engine on the basis of the intake air amount signal SM, the crank angle signal SC and the like. An ignition control signal Cq that corresponds to the normal ignition timing is supplied to the ignition timing control unit 22. As a result, the ignition coil unit 2
A secondary high-voltage pulse having a timing corresponding to the ignition control signal Cq is obtained from 3 and supplied to the spark plug 11 via the distributor 20. And
The spark plug 11 emits a spark in accordance with the ignition timing set by the ECU 24 to ignite the air-fuel mixture in the combustion chamber 10.

The ignited air-fuel mixture is discharged as exhaust gas from the combustion chamber 10 into the exhaust passage 9, purified by the three-way catalytic converter 18, and then discharged to the outside. Next, ECU
The electrical configuration of 24 will be described with reference to FIG. It should be noted that FIG. 1 shows only the configuration relating to the energization control and abnormality determination of the heater 16, and omits the configuration relating to the fuel injection control and ignition timing control shown in FIG.

As shown in FIG. 1, the ECU 24 includes a microcomputer (hereinafter abbreviated as “microcomputer”) 28, a buffer 29, and a heater energizing circuit 30. The heater energizing circuit 30 includes the heater 16 described above. It is connected. The microcomputer 28 includes an A / D converter that inputs signals from various sensors, a ROM that stores various programs including processing routines described later, and a RAM that stores self-diagnosis results and is backed up by a power supply. ing.
Further, in the present embodiment, the microcomputer 28 constitutes an abnormality determining means, and the microcomputer 28, in accordance with the current flowing through the heater 16, causes an abnormality due to deterioration of the heater 16 or an abnormality in the heater control system (battery short circuit or the like). ) Is determined.

The heater energizing circuit 30 includes a heater energizing portion 31 for controlling energization of the heater 16, a shunt resistor RT as a current detecting resistor, and a connection point P (a connection point between the heater 16 and the shunt resistor RT). And a voltage level determination section 32 for determining the level of the detected voltage VHD.

More specifically, the heater energization section 31 is provided with a MOS transistor (hereinafter abbreviated as transistor) Tr1 as a switching element and a protection resistor RP. The heater energization section 31 of the heater 16 is turned on / off according to the on / off operation of the transistor Tr1. Control energization. The shunt resistance RT has a resistance value which is several to several tens of times the resistance value on the transistor Tr1 side (the resistance value of the transistor Tr1 and the resistance value of the protection resistance RP). The current value at the time of energization or interruption of the energization is detected as a voltage value.

That is, according to the configuration of FIG.
5, the heater 16, the protection resistor RP, and the transistor Tr1 are connected in series, and the shunt resistor RT is connected in series with the heater 16 and in parallel with the protection resistor RP and the transistor Tr1. Therefore, when the heater 16 is energized (when the transistor Tr1 is on), the detection voltage VHD is detected according to the resistance values of the transistor Tr1, the protection resistor RP, and the shunt resistor RT, and when the heater 16 is de-energized (transistor Tr1). Shunt resistance R)
The detection voltage VHD is detected according to the resistance value of T.

The voltage level determination unit 32 also includes comparators 33 and 34 and resistors R11 to R14 and R21 to R24. Then, the comparators 33 and 34 connect the connection point P
Detection voltage VHD and resistors R11 to R14, R21 to R24
The threshold values VTH1 and VTH2 set by are compared and determined, and output signals C1 and C2 corresponding to the determination result are output. Specifically, if VHD ≧ VTH1, the output signal C1 of one comparator 33 becomes L level (low level), and if VHD <VTH1, the output signal C1 becomes H level (high level). If VHD ≧ VTH2, the output signal C2 of the other comparator 34 becomes L level,
If VHD <VTH2, the output signal C2 becomes H level. Here, the relationship between the threshold values VTH1 and VTH2 is VTH1
> VTH2 (see Figure 7).

The heater 16 which is a resistance type load is deteriorated due to factors such as aging.
The deterioration of No. 6 will be described. That is, as shown in FIG. 3, as the deterioration of the heater 16 progresses, its internal resistance increases and the current value flowing through the heater 16 decreases. Then, the deterioration of the heater 16 causes a decrease in the heating temperature of the heater 16, which may cause a problem of poor activation of the oxygen sensor 17. Therefore, in this embodiment, deterioration of the heater 16 is detected as a decrease in the detection voltage VHD.

Next, the operation of this embodiment will be described with reference to FIGS. 4 to 6 are processing routines executed by the microcomputer 28. The heater control routine of FIG. 4 has a cycle of 16 ms, the heater control system abnormality determination routine of FIG. 5 has a cycle of 128 ms, and the heater deterioration detection of FIG. The routine is executed every 64 ms. In each routine, a flag F is used to indicate various abnormal states.
1 to F6 are used. Of these, flags F1 to F3 indicate flags relating to abnormality of the heater control system (F1: battery short-circuit flag, F2: heater control system abnormality flag, F3: normal flag), and flags F4 to F6 indicate abnormality associated with deterioration of the heater 16. Related flags (F4: large heater deterioration flag, F5: small heater deterioration flag, F6: normal flag).

When the heater control routine of FIG. 4 is started, the microcomputer 28 first sets the battery short circuit flag F1, the heater control system abnormality flag F2, and the heater deterioration large flag F4 in step 101 (F1 = 1, 1). F2 = 1,
It is determined whether or not F4 = 1). If all the flags are cleared (F1 = 0, F2 = 0, F4 = 0), the microcomputer 28 proceeds to step 102. The processing related to the flags F1, F2, F4 will be described later.

At step 102, the microcomputer 28 increments the counter value K provided in the microcomputer 28 by "1". The number of executions of this routine is measured by this counter value K.

Thereafter, the microcomputer 28 proceeds to step 103.
Then, it is determined whether or not the engine speed Ne calculated based on the crank angle signal SC at that time is 6000 rpm or less. This determination process is for confirming that the energization condition of the heater 16 is satisfied, and Ne ≦ 6.
If it is 000 rpm, the microcomputer 28 considers that the energization condition is satisfied and moves to step 104.

At step 104, the microcomputer 28 determines whether or not the counter value K measured at step 102 is equal to or larger than a predetermined value K0. If K <K0, the microcomputer 28 proceeds to step 105 and the heater 1
6 is turned on (energized). The energization of the heater 16 heats the oxygen sensor 17.

On the other hand, in step 101, F1, F2,
Any of F4 is in the set state (F1 = 1, F2 = 1, F
4 = 1) or Ne> 600 in step 103.
0 rpm or K ≧ K0 in step 104
If so, the microcomputer 28 proceeds to step 106.
Then, the microcomputer 28 determines in step 106 the heater 16
Turn off (turn off the power).

In this way, the ON (energization) timing and the OFF (energization interruption) timing of the heater 16 are set according to the counter value K. Then, in the following operation of the microcomputer 28, the heater control system abnormality determination process is executed when the heater 16 is on, and the heater deterioration detection process is executed when the heater 16 is off.

On the other hand, when the heater control system abnormality determination routine of FIG. 5 is started, the microcomputer 28 first executes step 20.
At 1, it is determined whether or not the heater 16 is currently on (energized). If the heater is on, the process proceeds to step 202 and the subsequent control system abnormality determination processing is executed.

That is, the microcomputer 28 proceeds to step 202.
Then, it is determined whether or not the large heater deterioration flag F4 is set (F4 = 1). Then, the microcomputer 28 uses the F4
= 1, it is considered that the heater deterioration is large, and the routine is terminated. If F4 = 0, the heater deterioration is considered small, and the routine proceeds to step 203.

Thereafter, the microcomputer 28 proceeds to step 203.
Then, it is determined whether or not the battery voltage VB is equal to or higher than a predetermined voltage (10 volts in this embodiment). This determination process is
This is for confirming that the detection condition of the detection voltage VHD is satisfied, and if VB ≧ 10 V, the microcomputer 28 considers that the detection condition is satisfied and the step 2
Move to 04. Further, the microcomputer 28 executes the step 2
In 04, it is determined whether Ne ≦ 6000 rpm, and N
If e ≦ 6000 rpm, the process proceeds to step 205.

In subsequent steps 205 and 206, the microcomputer 28 outputs the output signals C1 and C of the comparators 33 and 34.
The output level of 2 is determined. For details, see the microcomputer 28
At step 205, C1 = "H" and C2 = "
H ", that is, the detection voltage V at the connection point P
It is determined whether HD is less than the threshold value VTH2. or,
In step 206, the microcomputer 28 determines whether C1 = "H" and C2 = "L", that is, whether the detected voltage VHD is within the threshold range VTH2 to VTH1.

Then, C1 = "H", C2 = "H" (V
If HD <VTH2), the microcomputer 28 determines that the control system of the heater 16 is normal, and proceeds to step 209.
After setting the normality flag F3 (F3 = 1), the routine ends.

On the other hand, C1 = "H", C2 = "L" (VTH
If 2 ≤ VHD ≤ VTH1), the microcomputer 28 proceeds to step 208 and determines that an abnormality has occurred in the heater control system and sets the heater control system abnormality flag F2 (F2 =
1) Do. Also, C1 = "L", C2 = "L"(VHD> V
If TH1), the microcomputer 28 proceeds to step 207 and considers that a short circuit has occurred in the battery 25 and sets the battery short circuit flag F1 (F1 = 1).

After the processing of steps 207 and 208, the microcomputer 28 proceeds to step 210 and the heater 1
After fixing 6 to the off (energization cutoff) state, the routine ends. That is, when the flags F1 and F2 are set, it is considered that the heater 16 cannot be controlled due to a battery short circuit or a heater control system abnormality, and the heater control is forcibly stopped.

On the other hand, when the heater deterioration detection routine of FIG. 6 is started, the microcomputer 28 first determines in step 301 whether or not the heater 16 is currently off (energization cutoff). Then, if the heater is off, the microcomputer 28 proceeds to step 302 and executes the subsequent heater deterioration detection processing.

That is, the microcomputer 28 executes the step 302.
Then, it is determined whether the battery short-circuit flag F1 or the heater control system abnormality flag F2 is set (F1 = 1 or F2 = 1). If both the flags F1 and F2 are cleared (F1 = 0, F2 = 0), the microcomputer 28 determines that there is no short circuit in the battery 25 and no abnormality in the heater control system, and proceeds to step 303.

Thereafter, the microcomputer 28 proceeds to step 303.
Determines whether or not VB ≥ 10 volts, and
In step 304, it is determined whether Ne ≦ 6000 rpm or not, and if both of the above conditions are satisfied, the process proceeds to step 305.

Subsequently, the microcomputer 28 proceeds to step 305.
In step 102 of FIG. 4, it is determined whether or not the counter value K measured is greater than or equal to a predetermined value K0, and in step 306, it is determined whether or not the counter value K is greater than or equal to a limit value (K0 +10). . Then, K0 ≤ K <(K0 +1
If 0), the microcomputer 28 proceeds to step 307.

That is, when K ≧ K0, the heater 16 is turned off (energization cutoff) in step 106 of FIG. 4, but immediately after that, when Ne> 6000 rpm, steps 101 → 102 → 103 → 106 in FIG. Is repeatedly executed, and the heater 16 remains off. When the heater is turned off, the heater temperature decreases, and if the outputs of the comparators 33 and 34 are determined in that state, there is a risk of erroneous detection. Therefore, when the heater is turned off for a predetermined time or more, the deterioration detection process is stopped by the process of step 306.

Further, in subsequent steps 307 and 308, the microcomputer 28 outputs the output signal C of the comparators 33 and 34.
The output levels of 1 and C2 are determined. Specifically, the microcomputer 28 determines in step 306 that C1 = “L” and C2.
= "L", that is, whether the detection voltage VHD exceeds the threshold value VTH1 is determined. In addition, the microcomputer 28
At step 307, C1 = "H" and C2 = "
L ", that is, the detection voltage VHD is the threshold value VTH
It is determined whether or not it is within the range of 2 to VTH1.

Then, C1 = "L", C2 = "L" (V
If HD> VTH1), the microcomputer 28 proceeds to step 311.
Then, the heater 16 is regarded as normal (no deterioration) and the normal flag F6 is set (F6 = 1). Also, C1 = "
If H ", C2 =" L "(VTH2 ≤ VHD ≤ VTH1), the microcomputer 28 proceeds to step 310 and the heater 1
Assuming that the deterioration of 6 is small, the heater deterioration small flag F5
Is set (F5 = 1).

After the processing in steps 310 and 311, the microcomputer 28 turns on (energizes) the heater 16 in step 313 and clears the counter value K to "0" in step 314. The heater deterioration small flag F
When 5 is set, that is, when a slight deterioration is confirmed, a predetermined warning means (for example, a warning light, a buzzer, etc.) prompts replacement of the heater 16.

On the other hand, C1 = "H", C2 = "H" (VHD
If <VTH2), the microcomputer 28 proceeds to step 309, considers that the heater 16 is largely deteriorated, sets the heater deterioration large flag F4 (F4 = 1), and turns off the heater 16 in the following step 312 ( Fix it to the "power off" state. That is, when the degree of deterioration of the heater 16 is large, the heater control is forcibly stopped.

Next, the operation of the microcomputer 28 will be described with reference to FIGS.
This will be described with reference to the timing chart of FIG. Figure 7
8 is a timing chart corresponding to the heater deterioration detection routine of FIG. 6 described above, where t11 to t12 and t13 to t of FIG.
The timings of 14 and t15 to t16 respectively indicate the heater off period (routine execution period of FIG. 6).

The detection voltage VHD changes depending on the ON / OFF state of the heater 16. That is, when the heater 16 is not deteriorated, the detected voltage VHD when the heater is off becomes larger than the threshold value VTH1 as shown in the timing of t11 to t12, and the output signals C1 and C1 of the comparators 33 and 34 are increased.
Both C2 are at the L level. At this time, the heater deterioration large flag F4 and the heater deterioration small flag F5 are in the reset state (F
4 = 0, F5 = 0), the normal flag F6 is held in the set state (F6 = 1).

When the heater 16 deteriorates and its internal resistance gradually increases, the output signal C1 of the comparator 33 becomes H level and the output signal C2 of the comparator 34 becomes L level as shown in the timing of t13 to t14. . At this time, as shown in FIG. 7, the deterioration level of the heater 16 is between large and small, and the small heater deterioration flag F5 is set (F5 = 1).

Further, when the deterioration of the heater 16 progresses and the internal resistance thereof becomes equal to or higher than a predetermined allowable value (large deterioration level of FIG. 7 or higher), as shown in the timing of t15 to t16,
The output signals C1 and C2 of the comparators 33 and 34 are both H
It becomes a level. At this time, the large heater deterioration flag F4 is set (F4 = 1), and the heater 16 is fixed to OFF after the timing of t15 when F4 = 1.

8 and 9 are timing charts corresponding to the heater control system abnormality determination routine of FIG. Among these, FIG. 8 shows an abnormality determination operation when the degree of abnormality is small (for example, contact failure of the soldered portion of the transistor Tr1 or the protection resistor RP), and FIG. 9 shows the abnormality determination operation when the degree of abnormality is large (for example, battery 25 shows a malfunction determination operation in a short circuit 25 or the like).

Now, in FIG. 8, before the timing of t21 (normal time), the detection voltage VHD when the heater is turned on is shown.
Is smaller than the threshold value VTH2, and the output signals C1 and C2 of the comparators 33 and 34 are both at the H level. Therefore, the flags F1 and F2 indicating the control system abnormality
Are cleared together (F1 is not shown).

When VTH2 ≤ VHD ≤ VTH1 is established due to contact failure in the soldered portion of the transistor Tr1 or the protective resistor RP at the timing of t21, the output signal C1 of the comparator 33 goes to H level and the comparator 34.
Output signal C2 of L level becomes L level. At this time, the heater control system abnormality flag F2 is set (F2 = 1), and the heater 16 is fixed to OFF.

On the other hand, in FIG. 9, before the timing of t31 (normal time), both the output signals C1 and C2 of the comparators 33 and 34 when the heater is turned on are high, as in FIG.
It is a level. Therefore, the flags F1 and F2 indicating the control system abnormality are both cleared (F2 is not shown).

Then, at the timing of t31, the battery 25
When VHD> VTH1 due to a short circuit, the output signals C1 and C2 of the comparators 33 and 34 both become L level. At this time, the battery short-circuit flag F1 is set (F1 = 1), and the heater 16 is fixed to OFF.

As described above in detail, in the abnormality detecting device in the load control device according to the present embodiment, when the heater 16 is off (energization cutoff), the detection voltage VHD corresponding to the current value of the heater 16 is a predetermined threshold. If the values are VTH1 and VTH2 or less, it is determined that an abnormality due to deterioration of the heater 16 has occurred. Further, when the heater 16 is turned on (energized), if the detected voltage VHD corresponding to the current value of the heater 16 is equal to or higher than the predetermined threshold values VTH1 and VTH2, an abnormality such as a short circuit occurs in the control system of the heater 16. I decided to judge.

With this configuration, it is possible to determine an abnormality due to deterioration of the heater 16 (load). Further, since the deterioration is determined when the energization of the heater 16 is cut off (when the transistor Tr1 is off), the current value of the heater 16 is detected without being affected by the loss of the on resistance of the transistor Tr1 and the like. The accuracy of the value detection is improved and the accuracy of the abnormality determination is improved.

Further, in this embodiment, the threshold value VTH1 for judging the detection voltage VHD corresponding to the current value of the heater 16 is used.
, VTH2 are set to two. Thus, the degree of deterioration of the heater 16 and the content of the control system abnormality of the heater 16 (abnormality of the transistor Tr1, short circuit of the battery 25, etc.) can be determined. Further, the detection condition of the detection voltage VHD is set by the battery voltage VB. This prevents erroneous detection of the detection voltage VHD and improves the abnormality detection accuracy.

Further, since the smoothing circuit having a large time constant as in the conventional abnormality detecting device is eliminated, problems such as delay in response are not caused. The present invention is not limited to the above embodiment, but may be embodied in the following modes.

For example, by providing three or more comparators in the voltage level determination section 32, three or more threshold values may be set. In this case, the degree of abnormality such as deterioration can be finely determined according to each threshold,
Judgment sensitivity is improved.

Further, in the above embodiment, the level of the detected voltage VHD corresponding to the current value of the heater 16 is compared with the comparator 33,
The result of comparison is fetched into the microcomputer 28 via the buffer 29, and the detected voltage VHD is A /
It is also possible to take in the microcomputer through the D converter and determine the level by software processing.

If the cause of the control system abnormality (battery short circuit or the like) is small, only the abnormality associated with the deterioration of the heater 16 may be detected. In this case, the configuration can be simplified.

Further, in the above-mentioned embodiment, the oxygen sensor heater of the resistance load is used as the load, but it is also applicable to the abnormality detection for another resistance load, for example, the LED.
It is also possible to detect abnormalities.

In addition, the load can be embodied as a coil type load (inductive type load). That is, it can also be applied to abnormality detection for a coil type load represented by a solenoid valve such as a fuel injection valve. However, in the case of the coil type load, the current is detected after the surge is eliminated immediately after the power supply is cut off.

[0073]

As described in detail above, according to the present invention,
An excellent effect that an abnormality due to deterioration of load can be determined and the abnormality determination accuracy can be improved is exhibited.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an ECU.

FIG. 2 is a configuration diagram showing an outline of a multi-cylinder spark ignition type gasoline engine.

FIG. 3 is a diagram for explaining deterioration of a heater.

FIG. 4 is a flowchart showing a heater control routine.

FIG. 5 is a flowchart showing a heater control system abnormality determination routine.

FIG. 6 is a flowchart showing a heater deterioration detection routine.

FIG. 7 is a timing chart regarding detection of heater deterioration.

FIG. 8 is a timing chart relating to abnormality determination of a heater control system.

FIG. 9 is a timing chart regarding abnormality determination of the heater control system, similarly to FIG.

[Explanation of symbols]

16 ... Heater as load, 25 ... Battery as power supply, 28 ... Microcomputer (microcomputer) as abnormality determining means, Tr1 ... Transistor as switching element, RT ... Shunt resistance as current detection resistor.

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G01N 27/409

Claims (4)

[Claims] 1. A load control device comprising a power source, a load, and a switching element connected in series so that the load is turned on or off in accordance with an on / off operation of the switching element. A current detection resistor connected in series with the load and in parallel with the switching element, and a current value of the load detected by the current detection resistor when the energization of the load is cut off is a predetermined value. An abnormality detection device in a load control device, comprising: an abnormality determination unit that determines that an abnormality has occurred in the load if the threshold value or less. 2. A load control device in which a power source, a load, and a switching element are connected in series, and the load is energized or cut off in accordance with an on / off operation of the switching element. A current detection resistor connected in series with the load and in parallel with the switching element, and a current value of the load detected by the current detection resistor when the energization of the load is cut off is a predetermined value. If the load value is equal to or less than a threshold value, it is determined that an abnormality has occurred in the load, and at the time of energization of the load, if the current value of the load is equal to or more than a predetermined threshold value, the control system of the load has an abnormality. An abnormality detection device in a load control device, comprising: abnormality determination means for determining that an abnormality has occurred. 3. The abnormality detection device in the load control device according to claim 1, wherein the threshold value for determining the current value of the load is provided in a plurality of stages. 4. The abnormality detection device in the load control device according to claim 1, wherein abnormality detection is prohibited when the voltage value of the power supply is equal to or lower than a predetermined value.